U.S. patent application number 16/476782 was filed with the patent office on 2019-12-12 for liquid-pressure driving system.
This patent application is currently assigned to KAWASAKI JUKOGYO KABUSHIKI KAISHA. The applicant listed for this patent is KAWASAKI JUKOGYO KABUSHIKI KAISHA. Invention is credited to Akihiro KONDO, Hiroaki MITSUI.
Application Number | 20190376535 16/476782 |
Document ID | / |
Family ID | 63039761 |
Filed Date | 2019-12-12 |
![](/patent/app/20190376535/US20190376535A1-20191212-D00000.png)
![](/patent/app/20190376535/US20190376535A1-20191212-D00001.png)
![](/patent/app/20190376535/US20190376535A1-20191212-D00002.png)
United States Patent
Application |
20190376535 |
Kind Code |
A1 |
MITSUI; Hiroaki ; et
al. |
December 12, 2019 |
LIQUID-PRESSURE DRIVING SYSTEM
Abstract
A liquid-pressure driving system includes: a pump connected to
an actuator through two pressure liquid passages; pressurizing
mechanisms interposed on the passages and applying pressure to the
operating oil returning from the actuator; a low pressure selector
valve connected to parts of the passages and introducing to a
cooling passage the operating liquid having lower pressure between
the operating liquids flowing through the two pressure liquid
passages; a restrictor mechanism interposed on the cooling passage;
a cooler apparatus interposed on the cooling passage downstream of
the restrictor mechanism, the cooler apparatus cooling the
operating liquid flowing through the cooling passage; and a
pressure liquid returning mechanism connected to parts of the two
pressure liquid passages, each of the parts being at one side of
the corresponding pressurizing mechanism close to the pump, the
pressure liquid returning mechanism returning the cooled operating
liquid to the two pressure liquid passages.
Inventors: |
MITSUI; Hiroaki; (Kobe-shi,
JP) ; KONDO; Akihiro; (Kobe-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KAWASAKI JUKOGYO KABUSHIKI KAISHA |
Kobe-shi, Hyogo |
|
JP |
|
|
Assignee: |
KAWASAKI JUKOGYO KABUSHIKI
KAISHA
Kobe-shi, Hyogo
JP
|
Family ID: |
63039761 |
Appl. No.: |
16/476782 |
Filed: |
January 26, 2018 |
PCT Filed: |
January 26, 2018 |
PCT NO: |
PCT/JP2018/002471 |
371 Date: |
July 9, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F15B 7/006 20130101;
F15B 2211/613 20130101; F15B 2211/27 20130101; F15B 2211/615
20130101; F15B 2211/7054 20130101; F15B 2211/20515 20130101; F15B
2211/611 20130101; F15B 2211/20561 20130101; F15B 2211/62 20130101;
F15B 11/08 20130101; F15B 21/0423 20190101; F15B 2211/40515
20130101; F15B 2211/7058 20130101; F15B 7/008 20130101; F15B 13/042
20130101; F15B 2211/428 20130101; F15B 13/0401 20130101; F15B
2211/20546 20130101; F15B 2211/41581 20130101; F04B 39/06
20130101 |
International
Class: |
F15B 21/0423 20060101
F15B021/0423; F15B 11/08 20060101 F15B011/08; F15B 13/04 20060101
F15B013/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2017 |
JP |
2017-016958 |
Claims
1. A liquid-pressure driving system in which a main circuit thereof
forms a liquid-pressure closed circuit together with a
liquid-pressure actuator, the liquid-pressure driving system
comprising: a liquid-pressure pump connected to the liquid-pressure
actuator through two pressure liquid passages and configured to
suck a pressure liquid through one of the two pressure liquid
passages and eject the pressure liquid through the other of the two
pressure liquid passages; pressurizing mechanisms interposed on the
respective two pressure liquid passages and configured to apply
pressure to the operating oil returning from the liquid-pressure
actuator; a low pressure selector valve connected to parts of the
two pressure liquid passages, each of the parts being located at
one side of the corresponding pressurizing mechanism which side is
close to the liquid-pressure actuator, the low pressure selector
valve being configured to introduce to a cooling passage the
operating liquid having lower pressure between the operating
liquids flowing through the two pressure liquid passages; a
restrictor mechanism interposed on the cooling passage; a cooler
apparatus interposed on the cooling passage so as to be located
downstream of the restrictor mechanism, the cooler apparatus being
configured to cool the operating liquid flowing through the cooling
passage; and a pressure liquid returning mechanism connected to
parts of the two pressure liquid passages, each of the parts being
located at one side of the corresponding pressurizing mechanism
which side is close to the pressure liquid pump, the pressure
liquid returning mechanism being configured to return the operating
liquid, cooled by the cooler apparatus, to the two pressure liquid
passages.
2. The liquid-pressure driving system according to claim 1,
wherein: the pressure liquid returning mechanism includes a
returning passage connected to the two pressure liquid passages;
and the returning passage is connected to the cooler apparatus.
3. The liquid-pressure driving system according to claim 2, further
comprising an accumulator connected to the returning passage,
wherein the accumulator maintains the operating liquid, flowing
through the returning passage, at preset set pressure.
4. The liquid-pressure driving system according to claim 1, wherein
the restrictor mechanism includes a variable restrictor configured
such that an opening degree thereof is changeable.
5. The liquid-pressure driving system according to claim 1,
wherein: the pressurizing mechanism includes a first check valve
and a second check valve; the first check valve is opened by the
operating liquid flowing from the liquid-pressure pump to the
liquid-pressure actuator; and the second check valve opens when
pressure of the operating liquid flowing from the liquid-pressure
pump to the liquid-pressure actuator becomes equal to or higher
than predetermined pressure.
6. The liquid-pressure driving system according to claim 1,
wherein: when differential pressure between liquid pressures of the
two pressure liquid passages becomes zero, the low pressure
selector valve is located at a neutral position; and at the neutral
position, the low pressure selector valve connects the two pressure
liquid passages to each other and also connects the two pressure
liquid passages to the cooling passage.
Description
TECHNICAL FIELD
[0001] The present invention relates to a liquid-pressure driving
system including a liquid-pressure pump constituting a closed
circuit together with a liquid-pressure actuator.
BACKGROUND ART
[0002] One example of an apparatus configured to supply pressure
oil to a hydraulic actuator, such as a hydraulic cylinder or a
hydraulic motor, to drive the hydraulic actuator is a hydraulic
continuously variable transmission. Known as the hydraulic
continuously variable transmission is a hydraulic driving apparatus
of PTL 1, for example. The hydraulic driving apparatus of PTL 1
includes a hydraulic pump. The hydraulic pump can switch an
ejection direction by changing a tilting angle of a swash plate
thereof. The hydraulic pump is connected to the hydraulic motor
through two main passages and constitutes a closed circuit together
with the hydraulic motor. In order to replace operating oil flowing
through the closed circuit with operating oil in a tank, the
hydraulic driving apparatus includes a low pressure selector valve,
a safety valve, and a charge pump. The low pressure selector valve
selects a main passage having lower pressure from the two main
passages and discharges the operating oil, flowing through the
selected main passage having the lower pressure, to the tank
through a relief valve. When the pressure in any of the main
passages becomes lower than predetermined oil pressure, the safety
valve connects this main passage to the charge pump and introduces
the operating oil, ejected from the charge pump, to this main
passage.
[0003] According to the hydraulic driving apparatus configured as
above, when the hydraulic pump is driven, the hydraulic pump sucks
the operating liquid from one of the main passages and ejects the
operating liquid to the other of the main passages. In this case,
the pressure of the one main passage becomes lower than the
pressure of the other main passage, and the operating oil of the
one main passage is discharged to the tank through the low pressure
selector valve and the relief valve. With this, a certain amount of
operating oil that is a part of the operating oil flowing through
the closed circuit is returned to the tank. Further, the pressure
of the one main passage becomes lower than the predetermined oil
pressure by the discharge of the operating oil, and the operating
oil is supplied from the charge pump to the one main passage. With
this, the operating liquid is introduced from the tank to the main
passage at a certain amount equal to the amount of operating oil
discharged. As above, according to the hydraulic driving apparatus,
the temperature of the operating oil flowing through the closed
circuit can be prevented from excessively increasing by returning a
certain amount of operating oil to the tank.
CITATION LIST
Patent Literature
[0004] PTL 1: Japanese Patent No. 5728621
SUMMARY OF INVENTION
Technical Problem
[0005] As described above, in the hydraulic driving apparatus of
PTL 1, the operating oil is returned to the main passage by the
charge pump. Therefore, various mechanisms are required for
providing the charge pump, and a space for accommodating these
mechanisms is also required. Since the hydraulic driving apparatus
includes the charge pump, the number of parts increases, and this
is a factor that increases the cost of the hydraulic driving
apparatus. Further, in the hydraulic driving apparatus, the
operating oil ejected from the charge pump when the actuator is in
a stop state is discharged to the tank through the safety valve at
all times. Therefore, energy loss of the hydraulic driving
apparatus is large.
[0006] An object of the present invention is to provide a hydraulic
driving system capable of cooling operating oil without using a sub
pump, such as a charge pump.
Solution to Problem
[0007] A liquid-pressure driving system of the present invention is
a liquid-pressure driving system in which a main circuit thereof
forms a liquid-pressure closed circuit together with a
liquid-pressure actuator. The liquid-pressure driving system
includes: a liquid-pressure pump connected to the liquid-pressure
actuator through two pressure liquid passages and configured to
suck a pressure liquid through one of the two pressure liquid
passages and eject the pressure liquid through the other of the two
pressure liquid passages; pressurizing mechanisms interposed on the
respective two pressure liquid passages and configured to apply
pressure to the operating oil returning from the liquid-pressure
actuator; a low pressure selector valve connected to parts of the
two pressure liquid passages, each of the parts being located at
one side of the corresponding pressurizing mechanism which side is
close to the pressure-liquid actuator, the low pressure selector
valve being configured to introduce to a cooling passage the
operating liquid having lower pressure between the operating
liquids flowing through the two pressure liquid passages; a
restrictor mechanism interposed on the cooling passage; a cooler
apparatus interposed on the cooling passage so as to be located
downstream of the restrictor mechanism, the cooler apparatus being
configured to cool the operating liquid flowing through the cooling
passage; and a pressure liquid returning mechanism connected to
parts of the two pressure liquid passages, each of the parts being
located at one side of the corresponding pressurizing mechanism
which side is close to the pressure liquid pump, the pressure
liquid returning mechanism being configured to return the operating
liquid, cooled by the cooler apparatus, to the two pressure liquid
passages.
[0008] According to the present invention, the low pressure
selector valve can connect the other of the two pressure liquid
passages to the cooling passage, and the pressurizing mechanism can
apply pressure to the operating oil returning from the
liquid-pressure actuator to the pressure liquid pump. With this,
the operating oil can be introduced to the cooling passage and can
be further introduced to the cooler apparatus through the cooling
passage. The restrictor mechanism is provided on the cooling
passage. Since the pressurizing mechanism applies pressure to the
operating oil returning to the pressure liquid pump, the operating
oil flows through the cooling passage at a certain flow rate
corresponding to the opening degree of the restrictor mechanism. To
be specific, when the liquid-pressure actuator is driving, the
operating oil can continuously flow through the cooler apparatus at
the certain flow rate. The operating liquid cooled by the cooler
apparatus is returned to the oil passage by the pressure liquid
returning mechanism. Therefore, the operating liquid cooled by the
cooler apparatus can be returned to the closed circuit. As above,
according to the liquid-pressure driving system, the operating oil
can be taken out from the closed circuit at the certain flow rate
and be cooled by the cooler apparatus, and the cooled operating oil
can be returned to the closed circuit. Therefore, a temperature
increase of the operating liquid in the closed circuit can be
suppressed. To be specific, according to the liquid-pressure
driving system, the operating oil can be supplied to and be cooled
by the cooler apparatus at the certain flow rate without using a
sub pump, and the operating oil can be returned to the oil passage
from the operating oil returning mechanism at the certain flow
rate. Therefore, a driving source of the sub pump and various
components can be omitted. Thus, the number of parts can be
suppressed, and the manufacturing cost can be suppressed. In
addition, since the sub pump is not used, the hydraulic driving
system can be reduced in size.
[0009] In the above invention, the pressure liquid returning
mechanism may include a returning passage connected to the two
pressure liquid passages, and the returning passage may be
connected to the cooler apparatus.
[0010] According to the above configuration, the hydraulic driving
system can be formed in a closed hydraulic circuit. With this,
foreign matters from outside can be prevented from getting into the
operating oil.
[0011] In the above invention, the liquid-pressure driving system
may further include an accumulator connected to the returning
passage. The accumulator may maintain the operating liquid, flowing
through the returning passage, at preset set pressure.
[0012] According to the above configuration, the liquid pressure of
the returning passage is maintained at the set pressure by the
accumulator. With this, the hydraulic pump can easily draw the
pressure liquid to the oil passage, and a sucking ability of the
hydraulic pump can be prevented from deteriorating.
[0013] In the above invention, the restrictor mechanism may include
a variable restrictor configured such that an opening degree
thereof is changeable.
[0014] According to the above configuration, the flow rate of the
operating oil introduced to the cooling passage can be adjusted by
changing the opening degree of the variable restrictor.
[0015] In the above invention, the pressurizing mechanism may
include a first check valve and a second check valve. The first
check valve may be opened by the operating liquid flowing from the
liquid-pressure pump to the liquid-pressure actuator. The second
check valve may open when pressure of the operating liquid flowing
from the liquid-pressure pump to the liquid-pressure actuator
becomes equal to or higher than predetermined pressure.
[0016] According to the above configuration, pressure can be
applied to the operating liquid returning from the liquid-pressure
actuator to the hydraulic pump.
[0017] In the above invention, when differential pressure between
liquid pressures of the two pressure liquid passages becomes zero,
the low pressure selector valve may be located at a neutral
position. At the neutral position, the low pressure selector valve
may connect the two pressure liquid passages to each other and also
connect the two pressure liquid passages to the cooling
passage.
[0018] According to the above configuration, the liquid pressure of
the liquid-pressure actuator can be released to the cooling passage
through the pressure liquid passage and the low pressure selector
valve. With this, the liquid-pressure actuator can be
depressurized.
Advantageous Effects of Invention
[0019] According to the present invention, operating oil can be
cooled by a hydraulic pump without using a sub pump.
[0020] The above object, other objects, features, and advantages of
the present invention will be made clear by the following detailed
explanation of preferred embodiments with reference to the attached
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a circuit diagram schematically showing a
hydraulic driving system of Embodiment 1.
[0022] FIG. 2 is a circuit diagram schematically showing the
hydraulic driving system of Embodiment 2.
DESCRIPTION OF EMBODIMENTS
[0023] Hereinafter, hydraulic driving systems 1 and 1A according to
embodiments of the present invention will be described with
reference to the drawings. It should be noted that each of the
hydraulic driving systems 1 and 1A described below is just one
embodiment of the present invention. Therefore, the present
invention is not limited to the embodiments. Additions, deletions,
and modifications may be made within the scope of the present
invention.
Embodiment 1
[0024] An industrial machine, such as a booster, a crusher, or a
carrier, includes a hydraulic actuator (i.e., a liquid-pressure
actuator) and can perform work by operating the hydraulic actuator.
The hydraulic actuator is, for example, a hydraulic cylinder 2 as
shown in FIG. 1, and the hydraulic cylinder 2 is constituted by a
double-acting hydraulic cylinder. To be specific, the hydraulic
cylinder 2 includes a piston 2a and two oil chambers 3 and 4
separated by the piston 2a. Therefore, according to the hydraulic
cylinder 2, when operating oil is supplied to the first oil chamber
3, the piston 2a moves toward a first side in a predetermined
direction. When the operating oil is supplied to the second oil
chamber 4, the piston 2a moves toward a second side in the
predetermined direction. The hydraulic cylinder 2 includes two
ports 2b and 2c. The first cylinder port 2b is connected to the
first oil chamber 3, and the second cylinder port 2c is connected
to the second oil chamber 4. A hydraulic driving system 1 is
connected to the hydraulic cylinder 2 so as to supply and discharge
the operating oil to and from the oil chambers 3 and 4 through the
cylinder ports 2b and 2c.
Hydraulic Driving System
[0025] In the hydraulic driving system 1, a main circuit 10 thereof
forms a closed circuit together with the hydraulic cylinder 2. The
hydraulic driving system 1 includes an electric motor 11, a
hydraulic pump 12, a variable displacement mechanism 13,
pressurizing mechanisms 14, a relief mechanism 15, a low pressure
selector valve 16, a variable restrictor mechanism 17, a filter 18,
a cooler apparatus 19, and an operating oil returning mechanism 20.
The electric motor 11 is a so-called servo motor or inverter motor
and is configured to be able to rotate an output shaft 11a thereof
in a normal direction and a reverse direction. The electric motor
11 is connected to a controller (not shown), and the controller
controls the rotational direction, rotational speed, rotation
amount, and the like of the output shaft 11a. The hydraulic pump 12
is coupled to the output shaft 11a.
[0026] The hydraulic pump 12 that is one example of a
liquid-pressure pump is a so-called swash plate variable
displacement pump and ejects the operating oil at an ejection flow
rate corresponding to a tilting angle of a swash plate 12a thereof.
The variable displacement mechanism 13 is provided at the swash
plate 12a. The variable displacement mechanism 13 changes the
tilting angle of the swash plate 12a in accordance with a signal
from the controller (not shown) to change the ejection flow rate of
the hydraulic pump 12. The hydraulic pump 12 includes two ports 12b
and 12c and ejects the operating oil from the port 12b or 12c in
accordance with the rotational direction of the output shaft 11a of
the electric motor 11. To be specific, when the output shaft 11a of
the electric motor rotates in the normal direction, the hydraulic
pump 12 sucks the operating oil through the first port 12b and
ejects the operating oil through the second port 12c. When the
output shaft 11a of the electric motor rotates in the reverse
direction, the hydraulic pump 12 sucks the operating oil through
the second port 12c and ejects the operating oil through the first
port 12b.
[0027] The first port 12b of the hydraulic pump 12 configured as
above is connected to the first cylinder port 2b of the hydraulic
cylinder 2 through a first oil passage 21, and the second port 12c
of the hydraulic pump 12 is connected to the second cylinder port
2c of the hydraulic cylinder 2 through a second oil passage 22.
Therefore, when the output shaft 11a of the electric motor rotates
in the normal direction, the hydraulic pump 12 sucks the operating
oil from the first oil chamber 3 of the hydraulic cylinder 2
through the first oil passage 21 and supplies the operating oil to
the second oil chamber 4 of the hydraulic cylinder 2 through the
second oil passage 22. With this, the piston 2a moves toward the
second side in the predetermined direction. On the other hand, when
the output shaft 11a of the electric motor rotates in the reverse
direction, the hydraulic pump 12 sucks the operating oil from the
second oil chamber 4 of the hydraulic cylinder 2 through the second
oil passage 22 and supplies the operating oil to the first oil
chamber 3 of the hydraulic cylinder 2 through the first oil passage
21. With this, the piston 2a moves toward the first side in the
predetermined direction. As above, the hydraulic pump 12 performs
the supply and discharge of the operating oil with respect to the
hydraulic cylinder 2 through the oil passages 21 and 22. The
pressurizing mechanisms 14 are interposed on the respective oil
passages 21 and 22.
[0028] In order to facilitate the sucking of the operating oil by
the hydraulic pump 12, each of the pressurizing mechanisms 14
applies pressure to, i.e., pressurize the operating oil sucked from
the hydraulic cylinder 2 to the hydraulic pump 12. More
specifically, each of the pressurizing mechanisms 14 includes a
first check valve 23 and a second check valve 24, and the first
check valve 23 and the second check valve 24 are interposed on the
oil passage (21 or 22) in parallel. To be specific, each of the oil
passages 21 and 22 branches and joins in the vicinity of the
pressurizing mechanism 14. The first check valve 23 and the second
check valve 24 are interposed on respective branched passage parts
of the oil passage (21 or 22). When the operating oil flows from
the hydraulic pump 12 to the hydraulic cylinder 2, the first check
valve 23 opens to allow the flow of the operating oil. When the
operating oil flows in the opposite direction, the first check
valve 23 remains closed to block the flow in the opposite
direction.
[0029] On the other hand, when the operating oil flows from the
hydraulic cylinder 2 to the hydraulic pump 12, the second check
valve 24 opens to allow the flow of the operating oil. When the
operating oil flows in the opposite direction, the second check
valve 24 remains closed to block the flow in the opposite
direction. Further, the second check valve 24 is a so-called
spring-equipped check valve. When the operating oil flows from the
hydraulic cylinder 2 to the hydraulic pump 12, but the pressure of
the operating oil is less than predetermined pressure, the second
check valve 24 remains closed. To be specific, when the pressure of
the operating oil flowing from the hydraulic cylinder 2 to the
hydraulic pump 12 is equal to or more than the predetermined
pressure, the second check valve 24 opens. With this, when the
hydraulic pump 12 sucks the operating oil from the hydraulic
cylinder 2 through the first oil passage 21, the second check valve
24 pressurizes the operating oil, which is returning to the
hydraulic pump 12 and flowing through an upstream side of the
second check valve 24 of the oil passage (21 or 22), to the
predetermined pressure or more. In the following description, the
pressurizing mechanism 14 interposed on the first oil passage 21
may be referred to as a pressurizing mechanism 14L, and the
pressurizing mechanism 14 interposed on the second oil passage 22
may be referred to as a pressurizing mechanism 14R.
[0030] These two pressurizing mechanisms 14L and 14R configured as
above constitute the above-described main circuit 10 together with
the two oil passages 21 and 22 and the hydraulic pump 12. The main
circuit 10 is connected to the hydraulic cylinder 2, and with this,
constitutes a closed circuit together with the hydraulic cylinder
2. In the main circuit 10 configured as above, the relief mechanism
15 is connected to the oil passages 21 and 22 so as to be located
upstream of the pressurizing mechanisms 14L and 14R.
[0031] When the oil pressure of the first oil passage 21 exceeds
relief pressure, the relief mechanism 15 discharges the operating
oil of the oil passage 21. When the oil pressure of the second oil
passage 22 exceeds the relief pressure, the relief mechanism 15
discharges the operating oil of the oil passage 22. To be specific,
the relief mechanism 15 includes a relief valve 25 and two check
valves 26 and 27. The relief valve 25 is connected to the two oil
passages 21 and 22 through a relief passage 28. More specifically,
the relief passage 28 connects the two oil passages 21 and 22 to
each other and branches, and the relief valve 25 is interposed on a
branched passage part 28a of the relief passage 28. The check valve
26 is interposed on the relief passage 28 so as to be located at
one side of a branch point 28b which side is close to the first oil
passage 21. The check valve 27 is interposed on the relief passage
28 so as to be located at the other side of the branch point 28b
which side is close to the second oil passage 22. The check valve
26 opens with respect to the flow of the operating oil from the oil
passage 21 to the relief valve 25 and closes with respect to the
flow in the opposite direction. The check valve 27 opens with
respect to the flow of the operating oil from the oil passage 22 to
the relief valve 25 and closes with respect to the flow in the
opposite direction. Therefore, the operating oil having higher
pressure between the operating oil flowing through the oil passage
21 and the operating oil flowing through the oil passage 22 is
introduced to the relief valve 25. When the pressure of the
operating oil introduced to the relief valve 25 exceeds the relief
pressure, the relief valve 25 opens the relief passage 28 to
discharge the operating oil. The relief passage 28 is connected to
a cooling passage 29 at a downstream side of the relief valve 25.
The low pressure selector valve 16 is connected to the cooling
passage 29. Further, the low pressure selector valve 16 is
connected between the pressurizing mechanism 14L of the first oil
passage 21 and a connecting point 28c of the relief passage 28 and
is also connected between the pressurizing mechanism 14R of the
second oil passage 22 and a connecting point 28d of the relief
passage 28.
[0032] The low pressure selector valve 16 is a valve configured to
select the operating oil having lower pressure from the operating
oil flowing through the first oil passage 21 and the operating oil
flowing through the second oil passage 22 and output the selected
operating oil having the lower pressure. To be specific, the low
pressure selector valve 16 includes three ports 16a to 16c. The
first port 16a is connected to the first oil passage 21. The second
port 16b is connected to the second oil passage 22, and the third
port 16c is connected to the cooling passage 29. Further, the low
pressure selector valve 16 includes a spool 16d, and the spool 16d
is configured to be movable in an axial direction thereof. The
spool 16d receives the oil pressure of the first oil passage 21 and
the oil pressure of the second oil passage 22 such that the oil
pressure of the first oil passage 21 and the oil pressure of the
second oil passage 22 act against each other. The spool 16d changes
its position in accordance with a differential pressure that is a
difference between the oil pressure of the first oil passage 21 and
the oil pressure of the second oil passage 22. According to the low
pressure selector valve 16, when the position of the spool 16d
changes, connection statuses of the three ports 16a to 16c
change.
[0033] More specifically, when the oil pressure of the first oil
passage 21 and the oil pressure of the second oil passage 22 are
equal to each other, the spool 16d is located at a neutral position
M. At the neutral position M, the three ports 16a to 16c are
connected to one another, and restrictors are formed with respect
to the first port 16a and the second port 16b. It should be noted
that the restrictors do necessarily not have to be formed and may
be omitted. With this, the oil pressure of the first oil passage 21
and the oil pressure of the second oil passage 22 can be kept equal
to each other after a small amount of time, and the oil pressure of
the oil chamber 3 and the oil pressure of the oil chamber 4 in the
hydraulic cylinder 2 can be reduced (i.e., the oil chambers 3 and 4
can be depressurized). On the other hand, when the oil pressure of
the second oil passage 22 is higher than the oil pressure of the
first oil passage 21, the spool 16d moves to a first offset
position A1. At the first offset position A1, the second oil
passage 22 is blocked, and the first oil passage 21 is connected to
the cooling passage 29. With this, the operating oil flowing
through the first oil passage 21 can be discharged to the cooling
passage 29. Further, when the oil pressure of the second oil
passage 22 is lower than the oil pressure of the first oil passage
21, the spool 16d moves to a second offset position A2. At the
second offset position A2, the first oil passage 21 is blocked, and
the second oil passage 22 is connected to the cooling passage 29.
With this, the operating oil flowing through the second oil passage
22 can be discharged to the cooling passage 29. The variable
restrictor mechanism 17 is interposed on the cooling passage 29,
through which the operating oil is discharged, so as to be located
upstream of a connecting point 29a where the cooling passage 29 and
the relief passage 28 are connected to each other.
[0034] The variable restrictor mechanism 17 is constituted by a
variable restrictor configured to be able to change the setting of
an opening degree thereof. The operating oil flows through the
cooling passage 29 at a downstream side of the variable restrictor
mechanism 17 at a flow rate corresponding to the opening degree set
in the variable restrictor mechanism 17 and differential pressure
before and after the variable restrictor mechanism 17. The filter
18 and the cooler apparatus 19 are interposed on the cooling
passage 29 so as to be located downstream of the connecting point
29a. The filter 18 removes foreign matters from the operating oil
flowing through the cooling passage 29. The cooler apparatus 19 is
a water-cooled or air-cooled oil cooler and cools the operating oil
introduced to the cooler apparatus 19 through the filter 18. The
operating oil returning mechanism 20 is provided at the cooling
passage 29.
[0035] The operating oil returning mechanism 20 returns the
operating oil, cooled by the cooler apparatus 19, to the passages
21 and 22. The operating oil returning mechanism 20 includes an
accumulator 30 and two check valves 31 and 32. The accumulator 30
is connected to the two oil passages 21 and 22 through a returning
passage 33. To be specific, the returning passage 33 connects a
part of the oil passage 21 which part is located at one side of the
pressurizing mechanism 14L which side is close to the hydraulic
pump 12 and a part of the oil passage 22 which part is located at
one side of the pressurizing mechanism 14R which side is close to
the hydraulic pump 12. Further, the returning passage 33 branches,
and the accumulator 30 and the cooling passage 29 are connected to
a branched passage part 33a of the returning passage 33. The check
valve 31 is interposed on the returning passage 33 so as to be
located at one side of a branch point 33b which side is close to
the first oil passage 21. The check valve 32 is interposed on the
returning passage 33 so as to be located at the other side of the
branch point 33b which side is close to the second oil passage 22.
The check valve 31 opens with respect to the flow of the operating
oil from the branch point 33b to the oil passage 21 and closes with
respect to the flow in the opposite direction. The check valve 32
opens with respect to the flow of the operating oil from the branch
point 33b to the oil passage 22 and closes with respect to the flow
in the opposite direction. The accumulator 30 is configured to be
able to accumulate preset set pressure (<predetermined pressure)
and maintains the oil pressure of the returning passage 33 at the
set pressure. With this, the operating oil cooled by the cooler
apparatus 19 easily returns to the passages 21 and 22 through the
returning passage 33.
Operations of Hydraulic Driving System
[0036] When the output shaft 11a of the electric motor 11 is
rotated by the controller (not shown) in, for example, the normal
direction, the hydraulic driving system 1 configured as above
functions as below. To be specific, the hydraulic pump 12 sucks the
operating oil from the first oil passage 21 and ejects the
operating oil to the second oil passage 22 at a flow rate
corresponding to the tilting angle of the swash plate 12a. The
ejected operating oil is introduced to the second oil chamber 4
through the second oil passage 22 and the first check valve 23 of
the pressurizing mechanism 14R, and the piston 2a moves toward the
second side in the predetermined direction. By the movement of the
piston 2a, the operating oil in the first oil chamber 3 is
discharged through the first cylinder port 2b to the first oil
passage 21. The operating oil discharged to the first oil passage
21 is introduced to the pressurizing mechanism 14L of the first oil
passage 21. The pressurizing mechanism 14L applies pressure by the
second check valve 24 (spring-equipped check valve) to the
operating oil flowing through the first oil passage 21 from the
hydraulic cylinder 2 to the hydraulic pump 12. When the pressure of
the operating oil becomes equal to or higher than the predetermined
pressure, the second check valve 24 opens, and the operating oil
flows from the hydraulic cylinder 2 to the hydraulic pump 12.
Therefore, the operating oil flowing through an upstream part of
the first oil passage 21 is pressurized to have the predetermined
pressure or more, i.e., a part of the first oil passage 21 which
part is located at one side of the pressurizing mechanism 14L which
side is close to the hydraulic cylinder 2 is pressurized to have
the predetermined pressure or more.
[0037] In the hydraulic driving system 1, when the operating oil is
ejected from the hydraulic pump 12 to the second oil passage 22,
the oil pressure of the second oil passage 22 becomes higher than
the oil pressure of the first oil passage 21, and the spool 16d of
the low pressure selector valve 16 moves to the first offset
position A1. Therefore, a part of the operating oil discharged to
the first oil passage 21 flows to the variable restrictor mechanism
17 of the cooling passage 29 through the low pressure selector
valve 16. At an upstream side of the variable restrictor mechanism
17, the predetermined pressure is maintained by the pressurizing
mechanism 14. At a downstream side of the variable restrictor
mechanism 17, the set pressure is maintained by the accumulator 30.
To be specific, the differential pressure before and after the
variable restrictor mechanism 17 is kept constant, and the variable
restrictor mechanism 17 supplies the operating oil to a downstream
side at a certain flow rate corresponding to the opening degree. As
above, the variable restrictor mechanism 17 can introduce the
operating oil from the first oil passage 21 to the cooling passage
29 at the certain flow rate corresponding to the opening degree.
The flow rate of the operating oil introduced can be changed by
changing the opening degree of the variable restrictor mechanism
17.
[0038] The operating oil introduced to the cooling passage 29 flows
through the filter 18 to reach the cooler apparatus 19, and is
cooled by the cooler apparatus 19. After the operating oil is
cooled by the cooler apparatus 19, the operating oil flows from the
cooling passage 29 to the returning passage 33. Regarding the two
oil passages 21 and 22 to which the returning passage 33 is
connected, the operating oil is sucked from the first oil passage
21 by the hydraulic pump 12, and the high-pressure operating oil is
ejected from the hydraulic pump 12 to the second oil passage 22.
With this, the oil pressure of the first oil passage 21 becomes
lower than the pressure (i.e., the set pressure) accumulated by the
accumulator 30, and the oil pressure of the second oil passage 22
becomes higher than the pressure (i.e., the set pressure)
accumulated by the accumulator 30. Therefore, only the check valve
31 out of the two check valves 31 and 32 opens, and the operating
oil introduced from the returning passage 33 returns to the first
oil passage 21 through the check valve 31 again. With this, the
operating oil cooled by the cooler apparatus 19 joins the operating
oil flowing through the pressurizing mechanism 14L. The operating
oil joined as above is sucked by the hydraulic pump 12 from the
first oil passage 21 and is ejected to the second oil passage 22 as
described above.
[0039] The hydraulic driving system 1 configured to operate as
above forms a hydraulic closed circuit together with the hydraulic
cylinder 2 as described above. Therefore, the hydraulic pump 12
ejects the operating oil at the flow rate basically equal to the
flow rate of the sucked operating oil. Further, the hydraulic
cylinder 2 discharges the operating oil from the third oil chamber
3 at the flow rate equal to the flow rate of the operating oil
supplied to the second oil chamber 4. On this account, when the
operating oil is introduced from the first oil passage 21 to the
cooling passage 29, the flow rate of the operating oil flowing
through the pressurizing mechanism 14 becomes smaller than the flow
rate of the sucked operating oil by the flow rate of the operating
oil introduced to the cooling passage 29. In order to compensate
the shortage of the operating oil, the operating oil is drawn from
the returning passage 33 to the first oil passage 21. Therefore,
the operating oil flows from the returning passage 33 to the first
oil passage 21 at the flow rate substantially equal to the flow
rate of the operating oil flowing from the first oil passage 21 to
the cooling passage 29, i.e., at the flow rate substantially equal
to the above-described certain flow rate. As above, when driving
the hydraulic cylinder 2, the operating oil can be cooled by the
cooler apparatus 19 at the certain flow rate, and the cooled
operating oil can be returned to the first oil passage 21. With
this, a temperature increase of the operating liquid in the closed
circuit can be suppressed.
[0040] The following will briefly describes a case where the output
shaft 11a of the electric motor 11 is rotated in the reverse
direction by the controller (not shown). In this case, the
operating oil flows in a direction opposite to the direction in
which the operating oil flows when the output shaft 11a rotates in
the normal direction. Then, the piston 2a moves toward the first
side in the predetermined direction. With this, the operating oil
is discharged from the second oil chamber 4, and the operating oil
discharged by the pressurizing mechanism 14R is pressurized to have
the predetermined pressure. Further, when the pressure of the first
oil passage 21 becomes high, the operating oil discharged from the
second oil chamber 4 is introduced to the variable restrictor
mechanism 17 of the cooling passage 29 through the low pressure
selector valve 16. As with when the output shaft 11a rotates in the
normal direction, the operating oil is discharged from the second
oil chamber 4 to the cooling passage 29 at the flow rate
corresponding to the opening degree of the variable restrictor
mechanism 17, and further flows through the filter 18 to reach the
cooler apparatus 19. The operating oil is cooled by the cooler
apparatus 19. Then, the operating oils flows through the check
valve 32, returns to the second oil passage 22 from the returning
passage 33, and joins the operating oil flowing through the
pressurizing mechanism 14R. The operating oil that joins as above
is sucked by the hydraulic pump 12 through the second oil passage
22 together with the operating oil flowing through the pressurizing
mechanism 14R, and is then ejected to the first oil passage 21 as
described above. As above, the operating oil flowing in the closed
circuit can flow to and be cooled by the cooler apparatus 19 at the
certain flow rate, and the cooled operating oil can be returned to
the second oil passage 22. With this, the temperature increase of
the operating liquid in the closed circuit can be suppressed.
[0041] As above, the hydraulic driving system 1 does not use a sub
pump, such as a charge pump included in a hydraulic driving
apparatus of conventional art. In the hydraulic driving system 1,
the operating oil can be supplied to the cooler apparatus 19 at the
certain flow rate, and the hydraulic pump 12 can return the
operating oil from the operating oil returning mechanism 20 at the
certain flow rate. Therefore, a driving source of the sub pump and
various components can be omitted. Thus, the number of parts can be
suppressed, and the manufacturing cost can be suppressed. In
addition, since the sub pump is not used, the hydraulic driving
system 1 can be reduced in size.
[0042] Although not shown, in the hydraulic driving system 1, for
example, a drain port of the hydraulic pump 12 and the returning
passage 33 are connected to each other. With this, the operating
oil leaking from various components in the hydraulic pump 12 is
introduced to the returning passage 33, and the operating oil is
also introduced to the returning passage 33 from portions other
than the first oil passage 21 and the second oil passage 22.
Further, since the oil pressure of the returning passage 33 is
maintained at the set pressure by the accumulator 30, the hydraulic
pump 12 can easily draw the operating oil from the returning
passage 33 to the oil passages 21 and 22. Therefore, a decrease in
sucking ability of the hydraulic pump 12 due to, for example, an
arrangement position of the returning passage 33 can be
suppressed.
[0043] In the hydraulic driving system 1, since the cooling passage
29 and the returning passage 33 are connected to each other, the
hydraulic driving system 1 can be formed in a closed hydraulic
circuit. With this, foreign matters from outside can be prevented
from getting into the operating oil.
[0044] In the hydraulic driving system 1, when the electric motor
11 stops, and therefore, the hydraulic pump 12 stops, the oil
pressure of the hydraulic passage 21 and the oil pressure of the
hydraulic passage 22 are balanced, and the piston 2a stops. Then,
the low pressure selector valve 16 returns to the neutral position
M, and the two hydraulic passages 21 and 22 are connected to each
other through the low pressure selector valve 16 and are also
connected to the cooling passage 29. With this, the oil pressure of
the oil chamber 3 and the oil pressure of the oil chamber 4 can be
released to the cooling passage 29 through the two oil passages 21
and 22. Thus, the oil chambers 3 and 4 can be depressurized.
Embodiment 2
[0045] The hydraulic driving system 1A of Embodiment 2 is similar
in configuration to the hydraulic driving system 1 of Embodiment 1.
Therefore, regarding the configuration of the hydraulic driving
system 1A of Embodiment 2, differences from the hydraulic driving
system 1 of Embodiment 1 will be mainly described. The same
reference signs are used for the same components, and a repetition
of the same explanation is avoided.
[0046] In the hydraulic driving system 1A of Embodiment 2, a
hydraulic motor 2A is connected to the first oil passage 21 and the
second oil passage 22. The hydraulic motor 2A that is one example
of the liquid-pressure actuator includes two supply/discharge ports
2d and 2e. When the operating oil is supplied to the first
supply/discharge port 2d, the hydraulic motor 2A rotates in the
normal direction. When the operating oil is supplied to the second
supply/discharge port 2e, the hydraulic motor 2A rotates in the
reverse direction. The hydraulic motor 2A rotates at a speed
corresponding to the flow rate of the operating oil supplied to one
of the supply/discharge ports 2d and 2e and discharges the
operating oil through the other of the supply/discharge ports 2e
and 2d at the flow rate substantially equal to the flow rate of the
supplied operating oil. The hydraulic motor 2A configured as above
rotates by receiving the supply of the operating oil from the
hydraulic driving system 1A.
[0047] The hydraulic driving system 1A is a so-called hydraulic
continuously variable transmission and forms a closed circuit
together with the hydraulic motor 2A. The hydraulic driving system
1A includes the electric motor 11, the hydraulic pump 12, the
variable displacement mechanism 13, the pressurizing mechanisms 14,
the relief mechanism 15, a low pressure selector valve 16A, the
variable restrictor mechanism 17, the filter 18, the cooler
apparatus 19, and an operating oil returning mechanism 20A. The low
pressure selector valve 16A is a value configured to select the
operating oil having lower pressure from the operating oil flowing
through the first oil passage 21 and the operating oil flowing
through the second oil passage 22. When the spool 16d is located at
the neutral position M, all the ports 16a to 16c are blocked.
[0048] In the hydraulic driving system 1A, the operating oil
returning mechanism 20A is connected to a tank 40 at a downstream
side of the cooler apparatus 19, and the operating oil cooled by
the cooler apparatus 19 is discharged to the tank 40. The returning
passage 33A is connected to the cooling passage 29 through the tank
40. The operating oil is drawn from the tank 40 to the returning
passage 33A by sucking force generated when the hydraulic pump 12
sucks the operating oil form each of the oil passages 21 and 22.
With this, the operating oil cooled by the cooler apparatus 19 can
be returned to each of the oil passages 21 and 22 through the tank
40. Further, two check valves 31 and 32 are interposed on the
returning passage 33A, and the operating oil returning mechanism
20A is constituted by these two check valves 31 and 32.
[0049] The hydraulic driving system 1A configured as above operates
in substantially the same manner as the hydraulic driving system 1
of Embodiment 1 except that: the operating oil cooled by the cooler
apparatus 19 is discharged to the tank 40; and when sucking the
operating oil by the hydraulic pump 12 from each of the oil
passages 21 and 22, a certain amount of operating oil is sucked
from the tank 40 through the returning passage 33A. The hydraulic
driving system 1A has the same operational advantages as the
hydraulic driving system 1 of Embodiment 1.
Other Embodiments
[0050] In each of the hydraulic driving systems 1 and 1A of
Embodiments 1 and 2, the electric motor 11 is used as a driving
source. However, the driving source is not necessarily limited to
the electric motor 11 capable of rotating in both directions. For
example, the driving source may be an electric motor, an engine, or
the like capable of rotating in one direction and is only required
to rotate the hydraulic pump 12. When using the driving source
capable of rotating its output shaft in one direction, such as the
electric motor or engine capable of rotating in one direction, the
hydraulic pump 12 configured as below is adopted. To be specific,
the hydraulic pump 12 is configured to be able to eject the
operating oil to the two ports 12b and 12c by changing the tilting
angle of the swash plate 12a.
[0051] In each of the hydraulic driving systems 1 and 1A of
Embodiments 1 and 2, the swash plate variable displacement pump is
adopted as the hydraulic pump 12. However, the hydraulic pump 12 is
not necessarily limited to such pump. For example, a fixed
displacement pump may be adopted as the hydraulic pump 12, or an
inclined shaft hydraulic pump may be adopted instead of a swash
plate hydraulic pump.
[0052] Each of the hydraulic driving systems 1 and 1A of
Embodiments 1 and 2 includes the accumulator 30 but does not
necessarily have to include the accumulator 30. When the
accumulator 30 is not included, the oil pressure of the returning
passage 33 decreases, and the sucking ability slightly
deteriorates, but the operating oil can be supplied to the cooler
apparatus 19.
[0053] From the foregoing explanation, many modifications and other
embodiments of the present invention are obvious to one skilled in
the art. Therefore, the foregoing explanation should be interpreted
only as an example and is provided for the purpose of teaching the
best mode for carrying out the present invention to one skilled in
the art. The structures and/or functional details may be
substantially modified within the scope of the present
invention.
REFERENCE SIGNS LIST
[0054] 1, 1A hydraulic driving system
[0055] 2 hydraulic cylinder
[0056] 2A hydraulic motor
[0057] 12 hydraulic pump
[0058] 14L, 14R pressurizing mechanism
[0059] 16 low pressure selector valve
[0060] 17 variable restrictor mechanism
[0061] 19 cooler apparatus
[0062] 20, 20A operating oil returning mechanism
[0063] 21 first oil passage
[0064] 22 second oil passage
[0065] 23 first check valve
[0066] 24 second check valve
[0067] 29, 29A cooling passage
[0068] 30 accumulator
[0069] 33, 33A returning passage
* * * * *